1. Field of the Invention
The present invention relates to a pellet-lifting apparatus which lifts pellets by means of lifting pins when the pellets located on a wafer sheet are picked up by a suction-adhesion nozzle.
2. Prior Art
In the past, an apparatus using a multiple number of peripheral lifting pins as described, for example, in Japanese Patent Application Laid-Open No. 62-98638, has been known as a means of lifting pellets in a stable manner.
In this apparatus, any change in the size of the pellets to be lifted necessitates a corresponding alteration in the arrangement and positioning of the peripheral lifting pins so that the pins will lift the pellets at the peripheral portions thereof. However, no consideration has been given to this point in prior art apparatuses.
In the abovementioned conventional apparatus, the peripheral lifting pins are inserted into peripheral pin insertion holes formed at prescribed positions in a pin holder to which the peripheral lifting pins are fastened. Then the peripheral lifting pins are fastened in place by screws. Accordingly, it is necessary to prepare a multiple number of pin holders so that the number of the holders corresponds to the number of different sizes of pellets that are to be handled. Furthermore, in cases where the central or peripheral lifting pins are broken for some reason, it is difficult to replace the pins.
Furthermore, the size of pin holders used for large pellets is often limited by the size of the surrounding parts. Moreover, since the peripheral lifting pins are positioned around the periphery of the pin holder, the screw holes, into which the screws for fastening the peripheral lifting pins are screwed, must be formed on the circumferential surface of the pin holder at points as far as possible from the peripheral pin insertion holes. In addition, the screw holes must be formed so that they do not intersect with each other. Thus, the pin fastening structure is extremely complicated.
In addition, the screws for fastening the peripheral lifting pins are usually small due to structural limitations inherent in the abovementioned pin holder. Thus, the tightening force of the screws is weak, which causes the peripheral lifting pins to fall out due to loosening of the screws.